1. Field of the Invention
The present invention relates generally to a metal hydride battery and more specifically relates to increasing the cycle life of a metal hydride battery by improving the battery hydrogen storage capability.
12. Background Art
Metal hydride batteries have been used in wide-ranging applications where a reliable, self-contained source of electric power is needed in a location which is generally inaccessible. U.S. Pat. No. 5,047,301, assigned to a subsidiary company of the assignee of the present invention, is drawn to a high temperature battery utilizing a connection between the battery and the source of hydrogen. That battery only begins operation when it is exposed to the hydrogen gas which passes through piping after the connection between the battery and the hydrogen source is made. The battery disclosed in U.S. Pat. No. 5,047,301 operates only so long as there is hydrogen being discharged from the hydrogen source, and stops operating when the flow of hydrogen either is discontinued or the hydrogen is depleted. This type of battery performs well in conditions where battery operation is necessarily automatic, such as in space or in a deep well environment, where manual intervention or monitoring is difficult, at best, and continued electrical power over long periods of time is not necessary.
These types of devices are further limited during use by the operation of the hydride battery, which is depleted of its electrical generating capacity as the hydrogen is absorbed within the cells of the battery. That is, when the battery cells absorb the available hydrogen to capacity or near to capacity, use of the battery no longer becomes possible without recharging of the battery cells by removal of the hydrogen.
Hydride batteries which are capable of regeneration have been described and used. Of particular significance in the hydrogen battery field, was the development of nickel-hydrogen (Ni--H.sub.2) systems on which extensive study has been performed.
A nickel hydrogen cell is disclosed in U.S. Pat. No. 3,850,694, utilizing a reversible electrolytic reaction wherein Ni(OH).sub.2 and OH.sup.- are converted to NiOOH, H.sub.2 0 and an electron. Reference to U.S. Pat. No. 3,850,694 is made for teaching of the electrochecmical process occurring in these types of batteries, and the subject matter of that patent is incorporated herein by reference. Because of the high initial cost of manufacture, implementation of Ni--H.sub.2 battery systems has not been cost-efficient except for certain esoteric uses, such as a power source in space.
Development of the Ni--H.sub.2 battery systems for terrestrial uses has been a subject of study by government agencies and private concerns. The search for an efficient and less costly alternative electrical battery has become more significant in recent times with the advent of electrical battery-powered automobiles. A clean source of power for automotive systems, such as electric power, is increasingly important in today's environment to avoid the resulting pollution, both noise and emission, which ensues from use of conventional gasoline combustion engines.
A major consideration of terrestrial use of hydride batteries is the costly initial funding of the materials needed to manufacture the battery and the need to charge and discharge the battery through a great number of cycles without succumbing to any appreciable loss of storage capacity or available potential and power.
As the hydride battery cycles through a discharge and recharge cycle, an appreciable amount of deterioration of the elements occurs. This deterioration is permanent and results from irreversible chemical processes within the storage and battery system. After repeated cycles, that deterioration is cumulative and results in failure of the system, requiring the complete replacement of the hydrogen storage unit, of the battery or of both. Replacement of these elements is an expensive proposition and consequently, preventing or postponing the deterioration of the elements in the system greatly prolongs battery cell operation without the need to expend excessive sums in replacing the deteriorated elements. The savings achieved in prolonged trouble-free operation are sufficient to provide a cost-effective utilization of hydride batteries in terrestrial applications, such as for providing a locomotive force in automobiles, which can more effectively compete on a total cost basis with conventional fuel systems such as internal combustion engines.
It has been found that the number of cycles in which a hydrogen storage vessel containing a metal hydride material can effectively store hydrogen is limited by the purity of the hydrogen being stored. Impurities in the hydrogen stream, such as water vapor or oxygen, greatly increase the deterioration rate of the metal hydride which absorbs and retains hydrogen in the storage vessel. During recharge of a hydride battery system, water vapor is entrained within the hydrogen that is being formed by the reverse electrolytic reaction. The oxygen contained in the water vapor "poisons" the metal hydride, which oxygen deteriorates the metal hydride material used for storing the hydrogen in a hydriding process.
A method of removing oxygen and water impurities from a hydrogen gas stream using a filter system is disclosed in U.S. Pat. No. 4,343,770. The system consists of an adsorbent for filtering out water from a hydrogen stream. The system which is disclosed further includes an elaborate network of piping and valve means for directing hydrogen flow through the filter means and into and out of the hydrogen consuming device, which, in the preferred embodiment, is an internal combustion engine utilizing gaseous hydrogen as the fuel.
Nickel hydride batteries, such as those disclosed in U.S. Pat. Nos. 3,850,964 and 5,047,301, as well as ambient temperature hydride batteries, which are generally available from Eagle Picher Industries of Joplin, Missouri, utilize an electrolyte which must be in a moist condition so as to maintain its conductivity. Great care must be taken with the amount of water available in the cell, as is discussed in U.S. Pat. No. 3,850,964. During battery discharge, the electrolytic reaction breaks down the gaseous hydrogen to form water, thus maintaining cell moisture.
However, during the recharging step, the battery cell produces gaseous hydrogen from the discharge reaction which also contains some evaporated water. Continued recharging of the battery drives out much of the water in the electrolyte and reduces the electrical generating capacity. The water condenses on the elements of the battery cell and maintains the conductivity of the electrolyte, which is necessary for the battery to continue providing electrical power. Thus, some means is necessary to maintain the moisture in the electrolyte by a mechanism which tends to force the water vapor toward the battery side of a separated hydrogen storage vessel/hydride battery cell.
In accordance with the above, there is disclosed a battery system and method of use thereof which utilizes a stream of hydrogen for generating electrical power on demand, comprising a hydrogen storage vessel having at least one opening and a metal hydride bed disposed therein, the metal hydride bed being able to absorb hydrogen under certain conditions and to release hydrogen under other conditions, a battery cell enclosed in an enclosure comprising an electrolyte and an oxidant, the enclosure of the battery cell having at least one opening, in-line piping means having at least two ends, one end being sealingly connected to the hydrogen storage vessel opening and the other end being sealingly connected to the battery cell opening, a predetermined quantity of hydrogen which is disposed within the system, whereby during discharging of the battery cell, the hydrogen is impelled to flow in a stream from the hydrogen storage vessel to the battery cell and during recharging of the battery cell, the hydrogen stream is impelled to flow from the battery cell to the hydrogen storage vessel, a catalytic converter disposed in-line between the battery battery cell and the hydride bend, and a molecular sieve dryer having a water adsorbing material for adsorbing water vapor from the stream of hydrogen during battery recharging and for releasing water as a vapor into the hydrogen stream during battery discharge, the molecular sieve dryer being disposed in line between the catalytic converter and the metal hydride bed.